Poaceae (Gramineae)

The Poaceae are mostly herbs comprising one of
the largest families of flowering plants with about 500 genera and 8,000 species. The
stems are round and commonly hollow, at least in the internodes. The leaves are alternate,
and commonly 2-ranked, proximally comprising an open sheathing base with overlapping
margins, and distally producing a parallel-veined, strap-shaped blade. On the adaxial leaf
surface at the junction of the blade and sheath is an often hairy fringe of tissue called
a ligule. The basic unit of the inflorescence is called a spikelet typically consisting of
a basal pair of minute sterile bracts called glumes and one or more distichously arranged
distal florets on an often zigzag extension of the spikelet axis called the rachilla. Each
floret is typically embraced by an additional pair of minute chaffy bracts called the
lemma and the palea. The florets are unisexual or bisexual and have usually two or three
barely recognizable structures called lodicules that may represent a vestigial whorl of
perianth that forces the lemma and palea apart during anthesis, thereby facilitating
exsertion of the stamens and stigmas. The androecium typically consists of three or
occasionally 6 distinct stamens. The gynoecium consists of a single compound pistil of 2
or sometimes 3 carpels, an equal number of styles with feathery stigmas, and a superior
ovary with one locule containing a single subapical to basal ovule. The fruit is usually a
caryopsis.

Each "thumbnail" image below is linked to a larger photograph.

Briza minor, quaking grass (Festucoideae-Poeae). Some of the
florets in these three spikelets have the stamens exserted. Festucoid grasses commonly
have more than one bisexual floret, and if they have any sterile florets, i.e. those
without pistils, they are situated above one or more fertile florets. The florets of the
spikelets are generally compressed from side to side rather than from front to back. When
the spikelets mature and disintegrate, the glumes mostly remain on the plant.

Sporobolus, indicus, West Indian dropseed, smutgrass
(Festucoideae-Eragrostideae). This genus is characterized by have small, 1-flowered
spikelets; the fruit usually falls free of the lemma and palea upon maturity.

Cynodon dactylon, Bermuda grass (Festucoideae-Cynodonteae). This
genus often has digitate inflorescences with sessile spikelets in 2 rows; the spikelets
have one basal fertile floret and often a terminal, sterile or vestigial floret.
Exserted yellowish stamens and reddish, feathery stigmas are clearly visible in the second
photo. Pendulous stamens that produce copious, dry, thin-walled pollen and stigmas that
are large and feathery are typical of wind pollinated plants and this is the most common
mode of pollination among grasses.

Chloris virgata, feather fingergrass (Festucoideae-Cynodonteae). This
genus has digitate inflorescences; the spikelets are secund in 2 rows, awned, bearing 1
basal, usually somewhat inflated fertile floret and 1-3 sterile distal florets. Note the
persistent glumes typical of Festucoid grasses on the axis at the left of the photo.

Cenchrus echinatus, sand bur (Panicoideae-Paniceae). In this case the florets
are enclosed by a cluster of numerous coalescing bristles that are very effective in
aiding dispersal of the fruits by tangling in the fur of animals or feathers of birds.

Melinus minutiflora, molasses grass (Panicoideae-Paniceae). The sterile lemma
of each floret has a long awn up to 1.5 cm in length.

Oplismenus compositus, (Panicoideae-Paniceae). This genus has the
spikelets in pairs; the glumes have awns up to 15 mm long.

Panicum maximum, Guinea grass (Panicoideae-Paniceae). The panicoid grasses typically have small spikelets, commonly consisting of a
single staminate or neuter floret at the base of the spikelet and a single bisexual,
fertile, terminal floret. At maturity, the entire spikelet usually separates from the
plant as a unit, including the glumes. Any compression of the florets in the spikelet is
usually from front to back rather than from side to side.

Paspalum fimbriatum, Panama or fimbriate paspalum, Colombia grass
(Panicoideae-Paniceae). In this genus the spikelets are in two rows and they exhibit
strong dorsi-ventral compression. The lemma of the fertile (terminal) floret is
indurate. As in most Panicoid grasses, the florets separate from the axis below the
glumes.

Pennisetum purpureum, elephant grass, napier grass (Panicoideae-Paniceae).
This robust species may reach 15 or more feet in height. The spikelets are
subtended by an involucre of numerous deciduous bristles up to 15 mm or longer.

Setaria gracilis, yellow foxtail (Panicoideae-Paniceae). The spikelets
are subtended by 1-several persistent, scabrous-barbellate bristles; disarticulation of
spikelets occurs between the glumes and the subtending bristles.

Coix lacryma-jobi, Job's tears, (Panicoideae-Andropogoneae).
This maize relative is naturalized in Hawaii and is sometimes cultivated as an ornamental.
The pearl-like accessory fruits are sometimes used for lei construction.

Heteropogon contortus, pili grass, twisted beardgrass, tanglehead
(Panicoideae-Andropogoneae). In this species each lemma may have an awn up to 12 cm
long; these are often twisted together in the upper part of the inflorescence.

Saccharum officinarum, sugar cane (Panicoideae-Andropogoneae).
Once a very important cash crop in Hawaii, cultivation of sugar cane is no longer
economically rewarding.

Sorghum halepense, Johnson grass (Panicoideae). This particular
tribe (Andropogoneae) of panicoid grasses typically has the spikelets in pairs (1 stalked,
1 sessile) along the axis. Both Panicoid and Festucoid grasses typically have a flap of
tissue called a ligule at the junction of the blade and sheathing portion of the leaf. In
this case the sheathing portion of the leaf has been pulled away from the stem to make the
ligule more visible. A fringe of hairs is often associated with the ligule.

Phragmites sp., (Arundinoideae)

Coraderia selloana, (Arundinoideae)

Oryza sativa, rice (Oryzoideae). This species is one of the most
important food crops that humans utilize, providing the primary source of starch for a
large segment of the world's population.

bamboo, (Bambusoideae). The bamboos are the only woody members of the
grass family. They also combine the most primitive characters occurring within the family,
such as florets with six stamens, and tricarpellate pistils.

Bambusa cf. vulgaris, bamboo.

Gigantochloa verticillata, bamboo (Bambusoideae). Note the
comparatively large spikelet, and florets with six exserted stamens.